There are a number of methods known in the art to increase the VI of lubricating oils such as hydroisomerization of linear paraffins present in the lubricating oils or by the addition of so-called VI-improvers: polymers which are added to an oil in order to improve its viscosity/temperature relationship.
It is, of course, possible to increase the molecular weight of a given molecule by subjecting it to a dimerization or oligomerization treatment. In order to achieve this normally rather reactive molecules and/or stringent conditions have to be applied. Moreover, the di- or oligomerization envisaged should be kept under control since otherwise products with undesirable or even unfavorable properties would be obtained in ever increasing amounts.
The use of electric discharges to change the molecular weight of hydrocarbons is another method and, of course, in principle well known. The production of ethylene, acetylene and carbon black from hydrocarbonaceous materials by subjecting them to electrical discharges has been extensively recorded in the literature and several processes have become commercial. It will be clear that such processes when starting from normally liquid hydrocarbonaceous materials are in essence cleavage processes, i.e., not only carbon-carbon bonds are ruptured but also carbon-hydrogen bonds in order to obtain molecules of lower molecular weight.
It is less frequently reported in the literature to increase the molecular weight of normally liquid hydrocarbonaceous materials by using electrical discharges. When the influence of an electrical discharge is described in the literature for such materials it becomes clear that rather reactive molecules have to be processed by using a specific form of electrical discharge, commonly referred to as a corona discharge. In U.S. Pat. No. 3,356,602 a process is described relating to the dimerisation of carboxylic acids by submitting them to a high electrical field (causing the occurrence of the so-called corona-discharge) together with a group 8 inert gas and/or hydrogen. It is clear from said specification that good results are only obtained in systems operating under alternate current and containing ethylenic unsaturation. Subjecting a saturated compound such as stearic acid to the process described in said U.S. Pat. No. 3,356,602 leads only to a fractional increase in molecular weight compared with related unsaturated compounds such as oleic acid and linoleic acid (see Table III of U.S. Pat. No. 3,356,602).
It would, therefore, be highly advantageous when the molecular weight of hydrocarbonaceous materials could be increased substantially in a controlled and controllable manner. It would be particularly advantageous when the viscosity and possibly the VI of lubricating base oils could be increased by means of an electric discharge, especially when such lubricating base oils would contain functional groups such as carboxylic groups, ester groups, amino groups, and/or amido groups which would continue to be present in substantial amounts in the thus treated lubricating base oils having an increased viscosity and, optionally VI. It would also be very advantageous when such functional groups could be incorporated into the structure of lubricating base oils not containing such functional groups (or only minor amounts thereof) during the process which allows an increase in viscosity and/or VI.